The present invention relates to a linear slide bearing and a linear slide table unit constructed by employing the same. More particularly, the invention pertains to a linear slide bearing and a linear slide table unit which are widely employed in the sliding part of various general industrial machines such as X-, Y- and Z-axes of numerical controlled machine tools, automatic tool changers, automatic welding machines, injection molding machines and industrial robots.
Hitherto, this kind of linear slide bearing has been composed of: a main body of substantially channel-like cross-section having a cavity formed on the lower side thereof; a track shaft having its upper part fitted in the cavity in the main body with a predetermined clearance therebetween; and a multiplicity of balls adapted to recirculate through two pairs of endless tracks formed on the main body. The balls recirculating through each pair of endless tracks are adapted to roll while clamping, from both sides, each of the ridges formed on both shoulder portions of the track shaft, thereby allowing the bearing to effect a linear reciprocation while bearing loads applied to the main body in vertical and radial directions.
In such a conventional linear slide bearing, however, it is necessary to form two pairs of endless tracks on the main body, and the track shaft must be formed with the number of raceway grooves corresponding to that of the endless tracks. In consequence, much labor is required for machining the main body and track shaft, particularly for forming the endless tracks and raceway grooves, resulting disadvantageously in a great increase in production cost.
Further, such a linear slide bearing is required to be incorporated with high accuracy into the sliding part of a general industrial machine. In addition, the bearing is required to be excellent in positioning and repetition accuracies as well as long in life. These characteristics are especially important for a linear slide table unit which performs a linear reciprocating motion while bearing a large load. It is also necessary to arrange the linear slide bearing so that it can easily display the above characteristics when incorporated in the table unit.
In such a linear slide bearing, however, if there is a clearance between raceways and balls which bear a load between the main body and the track shaft, an excessively large impact load is momentarily applied to the bearing by means of a hammering action or a prying and twisting load due to inertia moment at the time of a directional change in the reciprocating motion, thus causing a reduction in life. In addition, the positioning and repetition accuracies deteriorate in proportion to the amount of the clearance.
Accordingly, in the linear slide bearing of this kind, it is necessary to apply a preload to the bearing in order to make the above-mentioned clearance negative and increase the area of contact of each ball, so as to improve the load bearing capacity as well as enhancing the life and rigidity of the bearing. It is, therefore, desired that the linear slide bearing can be readily preloaded.